Since modern electronic devices such as television receivers have an increased number of functions, circuits of more complicated and higher integration have to be incorporated therein. In addition, these complicated circuits have to be protected against possible surge voltage by means of an electronic device such as varistor made of zinc-oxide. Therefore, the demand for varistors of this type is rapidly increasing.
A conventional zinc-oxide varistor can be manufactured by mixing zinc oxide with nickel, cobalt, and antimony compounds. These materials are molded into a compact which is then sintered at a temperature of 1150.degree. C. to 1350.degree. C. This sintered compact is then coated with electrode paste made of platinum or palladium and baked to form two electrodes thereon.
However, when antimony is added to the materials as an accessory constituent, the compact can not be sintered thoroughly at the above-mentioned temperature. Inability to thoroughly sinter the compact has been a primary problem of the conventional type of varistor.